Antioxidant and antimicrobial properties of polyphenolics from Withania adpressa (Coss.) Batt. against selected drug-resistant bacterial strains

Abstract

Withania adpressa (Coss.) Batt. (W. adpressa) is a wild medicinal plant in the family Solanaceae, which is used as an alternative medicine. The present study aims to investigate the chemical composition, antioxidant, and antibacterial potentials of polyphenol-rich fraction from the leaves of W. adpressa. Polyphenol-rich fraction was characterized by use of high-performance liquid chromatography (HPLC). Antioxidant potency was determined by use of 1,1-diphenyl-2-picrylhydrazyl (DPPH), ferric reducing antioxidant power (FRAP), and total antioxidant capacity (TAC) assays. Antibacterial activity was assessed against gram-positive and gram-negative bacteria by use of disc diffusion and microdilution assays. Chromatographic analysis by HPLC showed four compounds in the polyphenol-rich fraction including 1-O-Caffeoyl glucose, Luteolin-7-diglucuronide, Apigenin-O-pentoside, and Quercetin-3-O-glucuronide. Polyphenol-rich fraction exhibited important antioxidant activity as assessed by DPPH and FRAP assays, with IC50 and EC50 values of 14.27 ± 0.43 and 39.48 ± 0.81 μg/mL, respectively, while butylated hydroxytoluene (BHT) and Quercetin exhibited IC50 values of 28.92 ± 0.24 and 22.48 ± 0.54 μg/mL. Results of TAC showed that the polyphenol-rich fraction scored 781.74 ± 2.83 μg AAE/mg. Polyphenol-rich fraction showed an important antibacterial effect vs gram-positive and gram-negative strains recording inhibition zone diameters varying from 19.5 to 29.2 mm, while antibiotics were almost ineffective toward all strains except for E. coli. It can be concluded that W. adpressa polyphenol-rich fraction possesses promising phenols with strong antioxidant and antibacterial properties, which may help fight pathogenic bacteria and free radicals.